Oligomerization of liquid olefin over a nickel-containing silicaceous crystalline molecular sieve

ABSTRACT

A process for oligomerizing olefins in the liquid phase using nickel-containing silicaceous crystalline molecular sieve catalyst.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention is in the field of olefin oligomerization. Morespecifically, the present invention relates to oligomerization ofolefins in the liquid phase with a nickel-containing silicaceouscrystalline molecular sieve catalyst.

2. Description of the Prior Art

Oligomerization and polymerization of olefins in the gas phase overvarious zeolites is known in the art. For example, U.S. Pat. No.3,960,978 a process for producing a gasoline fraction containingpredominantly olefinic compounds which comprises contacting a C₂ to C₅olefin with a ZSM-5 type crystalline aluminosilicate zeolite at atemperature of from about 500° F. to about 900° F. as disclosed.

U.S. Pat. No. 4,021,501 describes the conversion of gaseous C₂ to C₅olefins into gasoline blending stock by passage over ZSM-12 attemperatures of from about 400° F. to about 1200° F.

U.S. Pat. No. 4,211,640 discloses a process for the treatment of highlyolefinic gasoline containing at least about 50% by weight of olefins bycontacting said olefinic gasoline with crystalline aluminosilicatezeolites, such as those of the ZSM-5 type, so as to selectively reactolefins other than ethylene and produce both gasoline and fuel oil.

U.S. Pat. No. 4,254,295 discloses a process for the oligomerization ofolefins by contacting said olefins in the liquid phase with ZSM-12catalyst at temperatures of 80° F. to 400° F.

U.S. Pat. No. 4,227,992 discloses a process for separating ethylene inadmixture with light olefins by contacting said olefinic mixture with aZSM-5 catalyst and thus producing both gasoline and fuel oil rangematerials.

The processes disclosed in these patents differ from that of the presentinvention in that they employ either a different catalyst, highertemperatures, or reaction in the gaseous phase.

Also, an important feature of several of the catalysts used in theseprior art processes is that the catalyst must have reduced activitybefore oligomerization. Such catalyst of reduced activity may beobtained by steaming or by use in a previous conversion process.

This deactivation step is not required in the process of the presentinvention.

SUMMARY OF THE INVENTION

In accordance with the present invention, there has been discovered aprocess for oligomerizing alkenes comprising: (a) contacting a C₂ to C₂₀olefin or mixture thereof in the liquid phase with a nickel-containingsilicaceous crystalline molecular sieve in the hydrogen form selectedfrom the group consisting of silicalite, an organosilicate disclosed inU.S. Pat. No. RE 29,948, CZM or mixtures thereof, at a temperature fromabout 45° F. to about 450° F.; (b) recovering an effluent comprisingoligomerized alkene.

It has been found that the present process provides selective conversionof the olefin feed to oligomer products. The present process effects theconversion of the olefin feed to dimer, trimer, tetramer, etc., productswith high selectivity. The product of the present reaction thus containsprimarily olefin oligomer and little or no light cracked products,paraffins, etc.

The high selectivity is in part due to the surprisingly higholigomerization activity of the catalyst of the present process, whichpermits high conversion at low temperatures where cracking reactions areminimized.

The oligomers which are the products of the process of this inventionare medium to heavy olefins which are highly useful for both fuels andchemicals. These include olefinic gasoline, such as from propylenedimerization, and extremely high quality midbarrel fuels, such as jetfuel. Higher molecular weight compounds can be used without furtherreaction as components of functional fluids such as lubricants, asviscosity index improvers in lubricants, as hydraulic fluids, astransmission fluids, and as insulating oils, e.g., in transformers toreplace PCB containing oils. These olefins can also undergo chemicalreactions to produce surfactants which in turn can be used as additivesto improve the operating characteristics of the compositions to whichthey are added (e.g., lubricating oils) or can be used as primarysurfactants in highly important activities such as enhanced oil recoveryor as detergents. Among the most used surfactants prepared from theheavy olefins are alkyl sulfonates and alkyl aryl sulfonates.

A significant feature of the present process is the liquid phasecontacting of the olefin feed and the nickel-containing silicaceouscrystalline molecular sieves. There will be appreciated that thepressures and temperatures employed must be sufficient to maintain thesystem in the liquid phase. As is known to those in the art, thepressure will be a function of the number of carbon atoms of the feedolefin and the temperature.

The oligomerization process described herein may be carried out as abatch type, semi-continuous or continuous operation utilizing a fixed ormoving bed catalyst system.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The feeds used in the process of the invention contain alkenes which areliquids under the conditions in the oligomerization reaction zone. Understandard operating procedures it is normal both to know the chemicalcomposition of feedstocks being introduced into a reaction zone and toset and control the temperature and pressure in the reaction zone. Oncethe chemical composition of a feedstock is known, the temperature andhydrocarbon partial pressures which will maintain all or part of thefeed as liquids can be determined using standard tables or routinecalculations. Conversely, once the desired temperature and pressure tobe used in the reaction zone are set, it becomes a matter of routine todetermine what feeds and feed components would or would not be liquidsin the reactor. These calculations involve using critical temperaturesand pressures. Critical temperatures and pressures for pure organiccompounds can be found in standard reference works such as CRC Handbookof Chemistry and Physics, International Critical Tables, Handbook ofTables for Applied Engineering Science, and Kudchaker, Alani, andZwolinski, Chemical Reviews 68, 659 (1968), all of which areincorporated herein by reference. The critical temperature for a purecompound is that temperature above which the compound cannot beliquefied regardless of pressure. The critical pressure is the vaporpressure of the pure compound at its critical temperature. These pointsfor several pure alkenes are listed below:

    ______________________________________                                                 T.sub.c °C.                                                                     (°F.)                                                                             P.sub.c -atm (bar)                               ______________________________________                                        ethene     9.21       (48.6)     49.66 (50.3)                                 propene    91.8       (197.2)    45.6 (46.2)                                  1-butene   146.4      (295.5)    39.7 (40.2)                                  1-pentene  191.59     (376.9)    40 (40.5)                                    iso-2-pentene                                                                            203        (397)      36 (36.5)                                    1-hexene   230.83     (447.49)   30.8 (31.2)                                  1-heptene  264.08     (507.34)   27.8 (28.2)                                  1-octene   293.4      (560.1)    25.6 (25.9)                                  1-decene   342        (648)      22.4 (22.7)                                  ______________________________________                                    

It can be appreciated that at temperatures above about 205° C. (401°F.), pure C₅ and lower alkenes must be gaseous, while pure C₆ and higheralkenes can still be liquefied by applying pressure. Similarly, aboveabout 275° C. (527° F.) pure C₈ and higher alkenes can be maintained inthe liquid state, while pure C₇ and lower alkenes must be gaseous.

Typical feeds are mixtures of compounds. But even so, once the chemicalcomposition of the feed is known, the critical temperature and pressureof the mixture can be determined from the ratios of the chemicals andthe critical points of the pure compounds. See for example, the methodsof Kay and Edmister in Perry's Chemical Engineers Handbook, 4th Edition,pages 3-214, 3-215 (McGraw Hill, 1963), which is incorporated byreference.

Of course, the only constraint on the alkenes present in the feed andwhich are to react in the oligomerization reaction zone is that thesealkenes be liquids under the conditions in the reaction zone (theconditions include a temperature of less than about 450° F.). Thechemical composition of the alkenes can be varied to obtain any desiredreaction mixture or produce mix, so long as at least some of the alkenecomponents of the feed are liquid.

The alkene chains can be branched. And, even though thenickel-containing silicaceous crystalline molecular sieve catalysts usedin this invention are intermediate pore size molecular sieves, alkeneshaving quaternary carbons (two branches on the same carbon atom) can beused. But where quaternary carbons are present, it is preferred that thebranches are methyl.

The preferred alkenes are straight chain, or n-alkenes, and thepreferred n-alkenes are l-alkenes. The alkenes have from 2 to 20 carbonatoms, and more preferably have from about 2 to about 6 carbon atoms.

One of the surprising discoveries of this invention is that undercertain reaction conditions, longer chain alkenes can be polymerizedinstead of being cracked to short chain compounds. Additionally, theoligomers produced from long n-l-alkenes are very highly desirable foruse as lubricants. The oligomers have surprisingly little branching sothey have very high viscosity indices, yet they have enough branching tohave very low pour points.

The feed alkenes can be prepared from any source by standard methods.Sources of such olefins can include FCC offgas, coker offgas, syngas (byuse of CO reduction catalysts), low pressure, nonhydrogenative zeolitedewaxing, alkanols (using high silica zeolites), and dewaxing withcrystalline silica polymorphs. Highly suitable n-l-alkene feeds,especially for preparing lubricating oil basestocks, can be obtained bythermal cracking of hydrocarbonaceous compositions which contain normalparaffins or by Ziegler polymerization of ethene.

Often, suitable feeds are prepared from lower alkenes which themselvesare polymerized. Such feeds including polymer gasoline from bulk H₃ PO₄polymerization, and propylene dimer, and other olefinic polymers in theC₄ -C₂₀ range prepared by processes known to the art.

The nickel-containing silicaceous crystalline molecular sieves used inthis invention are of intermediate pore size. By "intermediate poresize", as used herein, is meant an effective pore aperture in the rangeof about 5 to 6.5 Angstroms when the molecular sieve is in the H-form.Molecular sieves having pore apertures in this range tend to have uniquemolecular sieving characteristics. Unlike small pore zeolites such aserionite and chabazite, they will allow hydrocarbons having somebranching into the molecular sieve void spaces. Unlike larger porezeolites such as faujasites and mordenites, they can differentiatebetween n-alkanes and slightly branched alkanes on the one hand andlarger branched alkanes having, for example, quaternary carbon atoms.

The effective pore size of the molecular sieves can be measured usingstandard adsorption techniques and hydrocarbonaceous compounds of knownminimum kinetic diameters. See Breck, Zeolite Molecular Sieves, 1974(especially Chapter 8) and Anderson et al, J. Catalysis 58, 114 (1979),both of which are incorporated by reference.

Intermediate pore size molecular sieves in the H-form will typicallyadmit molecules having kinetic diameters of 5.0 to 6.5 Angstroms withlittle hindrance. Examples of such compounds (and their kineticdiameters in Angstroms) are: n-hexane (4.3), 3-methylpentane (5.5),benzene (5.8). Compound having kinetic diameters of about 6 to 6.5Angstroms can be admitted into the pores, depending on the particularsieve, but do not penetrate as quickly and in some cases are effectivelyexcluded. Compounds having kinetic diameters in the range of 6 to 6.5Angstroms include: cyclohexane (6.0), 2,3-dimethylbutane (6.1), m-xylene(6.1), and 1,2,3,4-tetramethylbenzene (6.4). Generally, compounds havingkinetic diameters of greater than about 6.5 Angstroms do not penetratethe pore apertures and thus are not absorbed into the interior of themolecular sieve lattice. Examples of such larger compounds include:o-xylene (6.8), hexamethylbenzene (7.1), 1,3,5-trimethylbenzene (7.5),and tributylamine (8.1).

The preferred effective pore size range is from about 5.3 to about 6.2Angstroms.

In performing adsorption measurements to determine pore size, standardtechniques are used. It is convenient to consider a particular moleculeas excluded if it does not reach at least 95% of its equilibriumadsorption value on the zeolite in less than about 10 minutes (p/po=0.5;25° C.).

Silicalite is disclosed in U.S. Pat. No. 4,061,724; the "RE 29,948organosilicates" are disclosed in U.S. Pat. No. RE 29,948; chromiasilicates, CZM, are disclosed in Ser. No. 450,419, Miller, filed Dec.16, 1982. These patents are incorporated herein by reference.

The crystalline silica polymorphs, silicalite, and U.S. Pat. No. RE29,948 organosilicates, and the chromia silicate, CZM are essentiallyalumina free.

"Essentially alumina free", as used herein, is meant the product silicapolymorph (or essentially alumina-free silicaceous crystalline molecularsieve) has a silica:alumina mole ratio of greater than 200:1, preferablygreater than 500:1. The term "essentially alumina free" is used becauseit is difficult to prepare completely aluminum free reaction mixturesfor synthesizing these materials. Especially when commercial silicasources are used, aluminum is almost always present to a greater orlesser degree. The hydrothermal reaction mixtures from which theessentially alumina free crystalline silicaceous molecular sieves areprepared can also be referred to as being substantially aluminum free.By this usage is meant that no aluminum is intentionally added to thereaction mixture, e.g., as an alumina or aluminate reagent, and that tothe extent aluminum is present, it occurs only as a contaminant in thereagents.

The most preferred molecular sieve is the zeolite Ni-silicalite. Ofcourse, these and the other molecular sieves can be used in physicaladmixtures.

When synthesized in the alkali metal form, the zeolites may beconveniently converted to the hydrogen form by well known ion exchangereactions, for example, by intermediate formation of the ammonium formas a result of ammonium ion exchange and calcination of the ammoniumform to yield the hydrogen form or by treatment with dilute acid such ashydrochloric acid.

Nickel is incorporated into these silicaceous crystalline molecularsieves according to techniques well known in the art such asimpregnation and cation exchange. For example, typical ion exchangetechniques would be to contact the particular sieve in the hydrogen formwith an aqueous solution of a nickel salt. Although a wide variety ofsalts can be employed, a particular preference is given to chlorides,nitrates and sulfates. The amount of nickel in the zeolites range from0.5% to 10% by weight and preferably from 1% to 5% by weight.

Representative ion exchange techniques are disclosed in a wide varietyof patents including U.S. Pat. Nos. 3,140,249; 3,140,251; 3,960,978,3,140,253 and 4,061,724.

Following contact with the salt solution, the zeolites are preferablywashed with water and dried at a temperature ranging from 150° F. toabout 500° F. and thereafter heated in air at temperatures ranging fromabout 500° F. to 1000° F. for periods of time ranging from 1 to 48 hoursor more.

The nickel-containing silicaceous crystalline molecular sieve catalystscan be made substantially more stable for oligomerization by includingfrom about 0.2% to 3% by weight and preferably 0.5% to 2% by weight ofthe Group IIB metals, zinc or cadmium and preferaby zinc. A primarycharacteristic of these substituents is that they are weak bases, andare not easily reduced. These metals can be incorporated into thecatalysts using standard impregnation, ion exchange, etc., techniques.Strongly basic metals such as the alkali metals are unsatisfactory asthey poison substantially all of the polymerization sites on thezeolite. For this reason, the alkali metal content of the zeolite isless than 1%, preferably less than 0.1%, and most preferably less than0.01%. The feed should be low in water, i.e., less than 100 ppm, morepreferably less than 10 ppm, in sulfur, i.e., less than 100 ppm andpreferably less than 10 ppm, in diolefins, i.e., less than 0.5%,preferably less than 0.05% and most preferably less than 0.01%, andespecially in nitrogen, i.e., less than 5 ppm, preferably less than 1ppm and most preferably less than 0.2 ppm.

The polymerization processes of the present invention are surprisinglymore efficient with small crystallite sieve particles than with largercrystalline particles. Preferably, the molecular sieve crystals orcrystallites are less than about 10 microns, more preferably less thanabout 1 micron, and most preferably less than about 0.1 micron in thelargest dimension. Methods for making molecular sieve crystals indifferent physical size ranges are known to the art.

The molecular sieves can be composited with inorganic matrix materials,or they can be used with an organic binder. It is preferred to use aninorganic matrix since the molecular sieves, because of their largeinternal pore volumes, tend to be fragile, and to be subject to physicalcollapse and attrition during normal loading and unloading of thereaction zones as well as during the oligomerization processes. Where aninorganic matrix is used, it is highly preferred that the matrix besubstantially free of hydrocarbon conversion activity. It can beappreciated that if an inorganic matrix having hydrogen transferactivity is used, a significant portion of the oligomers which areproduced by the molecular sieve may be converted to paraffins andaromatics and to a large degree the benefits of my invention will belost.

The reaction conditions under which the oligomerization reactions takeplace include hydrocarbon partial pressures sufficient to maintain thedesired alkene reactants in the liquid state in the reaction zone. Ofcourse, the larger the alkene molecules, the lower the pressure requiredto maintain the liquid state at a given temperature. As described above,the operating pressure is intimately related to the chemical compositionof the feed, but can be readily determined. Thus, the requiredhydrocarbon partial pressure can range from 31 bar at 450° F. for a puren-l-hexene feed to about atmospheric pressure for a n-l-C₁₅ -C₂₀ alkenemixture. In the process of this invention, both reactant and product areliquids under the conditions in the reaction zone, thus leading to arelatively high residence time of each molecule in the catalyst.

The reaction zone is typically operated below about 450° F. Above thattemperature not only significant cracking of reactants and loss ofoligomer product take place, but also significant hydrogen transferreactions causing loss of olefinic oligomers to paraffins and aromaticstake place. An oligomerization temperature in the range from about 90°F. to 350° F. is preferred. Liquid hourly space velocities can rangefrom 0.05 to 20, preferably from 0.1 to about 4.

Once the effluent from the oligomerization reaction zone is recovered, anumber of further processing steps can be performed.

If it is desired to use the long chain compounds which have been formedin middle distillate fuel such as jet of diesel or in the lube oils asbase stock, the alkene oligomers are preferably hydrogenated.

All or part of the effluent can be contacted with the molecular sievecatalyst in further reaction zones to further react unreacted alkenesand alkene oligomers with themselves and each other to form still longerchain materials. Of course, the longer the carbon chain, the moresusceptible the compound is to being cracked. Therefore, wheresuccessive oligomerization zones are used, the conditions in each zonemust not be so severe as to crack the oligomers. Operating witholigomerization zones in series can also make process control of theexothermic oligomerization reactions much easier.

One particularly desirable method of operation is to separate unreactedalkenes present in the effluent from the alkene oligomers present in theeffluent and then to recycle the unreacted alkenes back into the feed.

The following examples further illustrate this invention.

EXAMPLES Example 1

A Zn-silicalite catalyst was prepared in the following manner.H-silicalite of 240 SiO₂ /Al₂ O₃ mole ratio was mixed with peptized andneutralized Catapal alumina at a 67/33 sieve/alumina weight ratio,extruded through a 1/16" die, dried overnight at 300° F. under N₂, thencalcined in air for 8 hours at 850° F. The catalyst was impregnated bythe pore-fill method to 1 weight % Zn using an aqueous solution ofZn(NO₃)₂, then dried and calcined as done previously.

Example 2

The catalyst of Example 1 was impregnated to 3 weight % Ni by thepore-fill method using an aqueous solution of Ni(NO₃)₂.6H₂ O. Thecatalyst was dried overnight under N₂ at 300° F., then calcined in airfor 8 hours at 850° F.

Example 3

The Zn-silicalite catalyst of Example 1 was tested for convertingpropylene to higher molecular weight products at 150° F., 1000 psig, and0.5 LHSV. At 24 hours onstream, conversion to C₅ + was 3.2% with 38%selectivity to dimer.

Example 4

The Ni-Zn-silicalite catalyst of Example 2 was tested for convertingpropylene at the same conditions as in Example 3. At 40 hours onstream,conversion to C₅ + was 72.7% with 77% selectivity to dimer.

What is claimed is:
 1. A process for oligomerizing alkenescomprising:(a) contacting a C₂ to C₂₀ olefin or mixture thereof in theliquid phase with a nickel-containing silicaceous crystalline molecularsieve in the hydrogen form selected from the group consisting ofsilicalite, an organosilicate disclosed in U.S. Pat. No. RE 29,948, andCZM or mixtures thereof, at a temperature from about 45° F. to about450° F.; (b) recovering an effluent comprising oligomerized alkene. 2.The process of claim 1 wherein the nickel-containing silicaceouscrystalline molecular sieve also contains zinc cation.
 3. The process ofclaim 1 wherein said contacting is carried out at a LHSV of from about0.2 to
 5. 4. The process of claim 1 wherein the pressure is from about50 to about 1600 psig.
 5. The process of claim 1 wherein saidnickel-containing silicaceous crystalline molecular sieve is silicalite.6. The process of claim 1 wherein said nickel-containing silicaceouscrystalline molecular sieve is organosilicate disclosed in U.S. Pat. No.RE 29,948.
 7. The process of claim 1 wherein said nickel-containingsilicaceous crystalline molecular sieve is CZM.
 8. The process of claim5 wherein the nickel-containing silicaceous crystalline molecular sievealso contains zinc cation.
 9. The process of claim 6 wherein thenickel-containing silicaceous crystalline molecular sieve also containszinc cation.
 10. The process of claim 7 wherein said nickel-containingsilicaceous crystalline molecular sieve also contains zinc cation. 11.The process of claim 1 wherein said alkenes comprise n-alkenes.
 12. Theprocess of claim 15 wherein said n-alkenes are l-alkenes.
 13. Theprocess of claim 1 wherein said alkenes comprise branched chain alkenesand wherein the branches of said branched chain alkenes are methylbranches.
 14. The process of claim 1 further comprising the step ofhydrogenating said alkene oligomers.
 15. The process of claim 1 furthercomprising the steps of: separating unreacted alkenes present in saideffluent from alkene oligomers present in said effluent and recyclingsaid unreacted alkenes into the feed for said contacting step.